Field of the Invention
The invention relates to a method of producing a semiconductor component. In particular, the present invention relates to a method of producing a non-volatile memory cell with a switching transistor and a storage capacitor. The capacitor has plates which contain a platinum metal and a ferroelectric or paraelectric material is inserted between the plates as a dielectric.
Conventional microelectronic semiconductor memory components (DRAMs) essentially include a selection transistor or switching transistor and a storage capacitor, in which a dielectric material is inserted between two capacitor plates. Usually oxide or nitride layers which have a maximum dielectric constant of approximately 8 are mostly used as the dielectric. xe2x80x9cNovelxe2x80x9d capacitor materials (ferroelectrics or paraelectrics) with distinctly higher dielectric constants are required for reducing the size of the storage capacitor and for producing non-volatile memories. Some of those materials are named in a publication entitled xe2x80x9cNeue Dielektrika fxc3xcr Gbit-Speicherchipsxe2x80x9d [New Dielectrics for Gbit Memory Chips] by W. Hxc3x6nlein. Phys. Bl. 55 (1999). Ferroelectric materials, such as SrBi2 (Ta,Nb)2O9 (SBT or SBTN), Pb (Zr,Ti)O3 (PZT), or Bi4Ti3O12 (BTO), may be used as the dielectric between the capacitor plates for producing ferroelectric capacitors for applications in non-volatile memory components with high integration density. However, a paraelectric material, such as, for example, (Ba,Sr)TiO3 (BST), may also be used.
However, the use of those novel dielectrics, ferroelectrics or paraelectrics presents semiconductor process technology with new challenges. Firstly, those novel materials can no longer be combined with the traditional electrode material of polycrystalline silicon. Therefore, inert electrode materials such as, for example, platinum metals or their conductive oxides (for example RuO2), must be used. The reason for that is that, after the ferroelectric material has been deposited, it has to be annealed (xe2x80x9cconditionedxe2x80x9d), possibly several times, in an oxygen-containing atmosphere at temperatures of approximately 550-800xc2x0 C. In order to avoid undesired chemical reactions of the ferroelectric material with the electrodes, the latter are therefore mostly made from platinum or some other adequately temperature-stable and inert material, such as another platinum metal (Pd, Ir, Rh, Ru, Os).
Process steps which take place in a hydrogen-containing atmosphere are necessary for the integration of the storage capacitors. For example, for the conditioning of the metallization and of the transistors, annealing in forming gas which is composed of 95% nitrogen (N2) and 5% hydrogen (H2) is necessary. However, the penetration of hydrogen into the processed storage capacitor, i.e. into the dielectric, may lead to a degradation of the oxidic ceramics of the dielectric due to reduction reactions. Furthermore, the plasma-enhanced deposition of intermetal oxides (PECVD) or of the silicon nitride passivation layer may bring about a reduction of the ferroelectric or paraelectric material of the dielectric due to the high hydrogen content in the layers.
In the prior art, it has until now been attempted to solve the problem by depositing a passivation layer onto the storage capacitor. In U.S. Pat. No. 5,523,595, for example, a description is given of a method of manufacturing a semiconductor device in which a switching transistor is formed in a semiconductor substrate, a first insulating layer is deposited on the switching transistor, a ferroelectric storage capacitor coupled to the switching transistor is formed on the first insulating layer, a second insulating layer is applied above the storage capacitor and a barrier layer of TiON, resisting hydrogen penetration, is deposited on the second insulating layer. That previously known barrier layer has the effect of preventing the penetration of hydrogen through the upper electrode of the storage capacitor. However, diffusion of hydrogen through the first insulating layer, and of the lower electrode into the dielectric, continues to be possible and can consequently lead to a degradation of the storage capacitor. On the other hand, it is not possible to dispense with the hydrogen content in the forming gas, since free bonds (xe2x80x9cdangling bondsxe2x80x9d) in the semiconductor, in particular at the interfaces with the electrodes, and in the gate oxide are to be saturated by the hydrogen. In that situation, diffusion of the hydrogen through the lower electrode of the storage capacitor and subsequent damage to the ferroelectric cannot be ruled out.
It is accordingly an object of the invention to provide a method of producing a semiconductor memory, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods of this general type and in which a storage capacitor that uses a ferroelectric or paraelectric material for a dielectric can be adequately protected against penetration of hydrogen.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of producing a semiconductor component, which comprises:
a) forming a switching transistor on a semiconductor substrate;
b) embedding a first barrier layer, in particular resisting penetration of hydrogen, in an insulating layer and applying the insulating layer to the switching transistor;
c) forming a storage capacitor of a lower electrode, an upper electrode and a metal-oxide-containing layer deposited between the lower and upper electrodes, coupling the storage capacitor to the switching transistor and applying the storage capacitor to the insulating layer;
d) removing the insulating layer to a certain depth outside the storage capacitor in a vertical etching step, while exposing the first barrier layer to the outside; and
e) applying a second barrier layer, in particular resisting penetration of hydrogen, to the storage capacitor, to the insulating layer and to the first barrier layer.
The metal-oxide-containing layer in this case is preferably a ferroelectric or paraelectric material.
In accordance with another mode of the invention, the switching transistor is connected to the storage capacitor in such a way that, after the insulating layer is applied, a contact hole is etched into the latter as far as a terminal region of the switching transistor, for example a drain region of an MOS switching transistor, and is filled with a conductive material, and the lower electrode of the storage capacitor is subsequently applied at least partially to the contact hole.
In accordance with a further mode of the invention, before the contact hole is filled, it is lined on its inner wall surfaces with a third barrier layer, in particular resisting the penetration of hydrogen. As a result, the hydrogen can additionally be prevented from diffusing into the contact hole filled with the conductive material (xe2x80x9cplugxe2x80x9d) and penetrating through the conductive material of the contact hole and the lower electrode into the metal-oxide-containing layer. Consequently, the storage capacitor being produced is completely encapsulated by barrier layers.
In accordance with an added mode of the invention, in step d), the first insulating layer is removed to the depth of the first barrier layer, and it is possible, if appropriate, for the first barrier layer to be used as an etching stop layer. As an alternative to this, also in step d), the first insulating layer may be removed to a depth below the first barrier layer.
In accordance with an additional mode of the invention, the first barrier layer is produced from Si3N4, and a chemical gas phase deposition at low pressure (LPCVD) produces particularly good results. ZrO2 or SiO2/ZrO2 may also be chosen as the material of the first barrier layer. The materials which are known per se in the prior art Al2O3, TiO2, Ta2O5 may also be used as the material for the first barrier layer.
In accordance with yet another mode of the invention, in order to provide the third barrier layer, with which the inner wall surfaces of the contact hole etched into the first insulating layer are lined, in principle the same materials may be used as for the first barrier layer. If Si3N4 is chosen as the material for the third barrier layer, in this case too, the deposition preferably takes place by LCVD.
In accordance with yet a further mode of the invention, the second barrier layer, deposited on the storage capacitor, is made up of an SiOxxe2x80x94SiONxe2x80x94Si3N4 combination of layers. An SiOx layer is first grown on, preferably by CVD (chemical vapor deposition), an SiON layer is subsequently deposited, likewise preferably by CVD, and finally an Si3N4 layer is applied, preferably by LPCVD.
In accordance with a concomitant mode of the invention, in order to protect the ferroelectric or paraelectric material of the dielectric, as this takes place, from the relatively large amounts of hydrogen which occur during the LPCVD deposition of the Si3N4 layer, an oxidic or nitridic barrier layer (X layer) may be additionally deposited below the combination of layers or between individual layers of the combination of layers. The layer structure of the combination of layers is consequently, for example, Xxe2x80x94SiO2xe2x80x94SiONxe2x80x94Si3N4 or SiO2xe2x80x94Xxe2x80x94SiONxe2x80x94Si3N4. Ta2O5, Bi2O3, TiO2, Al2O3, Nb2O5, MgO, V2O5, CeO2, Y2O3, ZrO2, BN, AlN and all rare earth oxides may be used, for example, as the material for the X layer. Furthermore, in order to repair any damage to the ferroelectric or paraelectric as a consequence of the CVD deposition of the silicon oxide layer, an annealing step is also preferably performed after the SiOX deposition.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method of producing a ferroelectric semiconductor memory, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.